The present invention relates to an improved polarographic or other voltammetric flow through apparatus wherein improved results are obtained in the deoxygenation of the sample as well as the dampening of pump pulsations in the sample flow to provide decreased time required per analysis and improved test results.
As utilized herein, voltammetric analysis includes polarographic analysis. As used herein, polarographic analysis is voltammetric analysis utilizing a dropping mercury electrode. Voltammetric analysis is meant to refer herein to electrochemical analysis which utilizes an electrode other than a dropping mercury electrode. The present invention is applicable to both.
Electrochemistry utilizing the dropping mercury electrode polarography and other types of voltammetry is known in the art, for example see Polarography, Encyclopedia of Chemistry, 3rd Edition, published by Van Nostrand Reinhold Company, 1973. However, there has been a need in polarography, voltammetry, stripping voltammetry and linear sweep voltammetry to automate sample handling and deoxygenation, particularly when reductive electrochemical determinations are performed. Attempts to automate electrochemical techniques have failed to mechanize the sample handling steps one would do manually. Another problem with manual and the few attempts that automated electrochemical instruments which have been made is the potential exposure of the analyst to solvent vapors and mercury (if a dropping mercury electrode is used).
In some prior art devices, deoxygenation has been performed by bubbling an inert gas through the analyte for four to ten minutes. Vapors from volatile solvents and analytes are released into the laboratory atmosphere creating an exposure for the analyst. The four to ten minutes deoxygenation time lengthens the total analysis time as does manually filling and emptying electrochemical cells.
One attempt at automation is shown by U.S. Pat. No. 4,138,322--Barnes, et al. wherein nitrogen gas is injected into a glass helical coil through which the analyte passes forming bubbles in the flow. These bubbles are then ducted out of the system. In addition to the time factors involved, this may cause the loss of solvent or analyte, particularly where solvent and analyte are volatile. This reduces the accuracy and reproducibility of the electrochemical determination. Furthermore, the analyte may become contaminated during deoxygenation by leakage, since the inert gas is injected directly into the analyte flow stream. Furthermore, such a system does not provide pump pulsation dampening in the glass helical coil.
Other deoxygenation methods have included the use of a gas permeable tube mounted within a vacuum. For example, see German Democratic Republic patent No. DD 248,192 which utilizes a 40 cm. silicone rubber tube and a Smoler capillary and U.S. Pat. No. 4,469,495--Hiraizumi, et al. which utilizes a plurality of spiral turns with spacer elements therebetween in a tank which is under at least a partial vacuum. Other attempts have included the use of a nebulizer, for example see U.S. Pat. No. 4,500,411--Yarnitzky.
The present invention provides a significance improvement over prior art flow though voltammetry analysis apparatus including polarographic analysis apparatus.